The present invention relates to empty load devices for load-sensing and proportioning of brake signals on a rail car and more specifically to an empty-load device having separate load sensing and signal proportioning valve housings.
Some examples of empty-load devices currently in use are shown in U.S. Pat. Nos. 3,671,086 (Scott), 4,417,767 (Billeter) and 5,211,450 (Gayfer).
Billeter and Scott disclose what is known as SC-1 equipment, which has two portions: a sensor portion in a separate housing and a proportioning portion in a separate housing. Load sensing is effected by displacement of the rail car springs related to the rail car""s weight when empty and loaded. Generally, sensing occurs when the rail car""s springs deflect nominally more than 25% of the travel between empty-car and loaded-car conditions. The sensor mounted to the rail car body detects spring displacement and operates to pilot a proportioning valve with pressure from a brake cylinder. The difficulty with this SC-1 equipment is that, at the point of changeover braking from loaded-car to empty-car brake conditions, the brake cylinder pressure is directed to a proportioning valve through a downstream equalizing volume reservoir of nominally 600 cubic inches (cu. in.). At changeover, and because the brake cylinder pressure is directed through the 600 cu. in. equalizing volume, the brake cylinder pressure may stall or decrease until the downstream volume equalizes with the brake cylinder. In the event that the required brake cylinder pressure happens to occur at the changeover point, the brake cylinder pressure will always decrease as the equalizing volume fills.
Gayfer discloses moving the equalizing volume reservoir upstream from the brake cylinder in an empty-load device in a single housing.
The present invention provides for an empty-load system including a first housing having brake cylinder, control valve, equalization volume reservoir and pilot ports. Also included is a ratio means, in the first housing, having a ratio piston and a ratio valve for controlling the connection of the control valve port to the brake cylinder port and to the equalization port. Further included is a pilot piston in the first housing being responsive to a pilot pressure at the pilot port to operate the ratio valve. The empty-load system also includes a second housing having a brake cylinder port and a pilot port connected, respectively, to the brake cylinder port and the pilot port of the first housing. The second housing also includes a sensor means having a sensor piston for sensing the load of a railroad car and further includes a sensor valve connected to the sensor piston which connects the brake cylinder port to the pilot port for a first position of the sensor piston.